Selenium-induced changes in activities of antioxidant enzymes and content of photosynthetic pigments in Spirulina platensis

Spirulina platensis exposed to various selenium (Se) concentrations (0, 10, 20, 40, 80, 150, 175, 200, 250 mg/L) accumulated high amounts of Se in a dose- and time-dependent manner. Under low Se concentrations (<= 150 mg/L), Se induced increases in biomass concentration, content of photosynthetic pigments, and activities of glutathione peroxidase (GPX), superoxide dismutase (SOD), catalase (CAT) and Gua-dep peroxidases ( POD), which indicates that antioxidant enzymes play an important role in protecting cells from Se stress. Higher Se concentrations (>= 175 mg/L) led to higher Se accumulation and increases in activities of GPX, SOD, CAT and POD, but also induced lipid peroxidation (LPO) coupled with potassium leakage and decreases in biomass concentration and contents of photosynthetic pigment. The results indicate that increases in activities of the antioxidant enzymes were not sufficient to protect cell membranes against Se stress. Time-dependent variations in the activities of antioxidant enzymes, contents of chlorophyll a and carotenoid and the LPO level were also investigated under representative Se concentrations of 40 and 200 mg/L. Opposite variation trends between SOD-CAT activities, and GPX-POD-APX activities were observed during the growth cycles. The results showed that the prevention of damage to cell membranes of S. platensis cells could be achieved by cooperative effects of SOD-CAT and GPX-POD-APX enzymes. This study concludes that S. platensis possessed tolerance to Se and could protect itself from phytotoxicity induced by Se by altering various metabolic processes.